DataGridColumn with null field exception

[sturlath]

Hi

I have a multitenant system that reviles certain information if you are a tenant or not.

So in one case I want to display information in my host count that will have null values in them.

When its null, I will display "n/a" or something.

But I´m having problems with this here where EventPriceInfo on EventWithNavigationPropertiesDto in UpcomingEventList is null and therefore Field="EventPriceInfo.LivePrice" throws

  <DataGrid TItem="EventWithNavigationPropertiesDto"
        Data="UpcomingEventList"
        TotalItems="TotalCount"
        ShowPager="true"
        Responsive="true"
        PageSize="PageSize">
      <DataGridColumns>
         <DataGridColumn TItem="EventWithNavigationPropertiesDto"
                    Field="EventPriceInfo.LivePrice"
                    Caption="Price">
        </DataGridColumn>
      </DataGridColumns>
  </DataGrid>

with this code-behind

private IReadOnlyList<EventWithNavigationPropertiesDto> UpcomingEventList { get; set; } 

    public class EventWithNavigationPropertiesDto
    {
        public EventPriceInfoDto EventPriceInfo { get; set; }
    }

    public class EventPriceInfoDto : FullAuditedEntityDto<Guid>
    {
        public int LivePrice { get; set; }
    }

The error (btw was hard to find out what was causing this in the first place. Is it possible to add more data?)

Microsoft.AspNetCore.Components.WebAssembly.Rendering.WebAssemblyRenderer[100]
Unhandled exception rendering component: Object reference not set to an instance of an object.
System.NullReferenceException: Object reference not set to an instance of an object.
at Blazorise.DataGrid.DataGridColumn1[[EventWithNavigationPropertiesDto, Application.Contracts, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].GetValue(StreamEventWithNavigationPropertiesDto item) at Blazorise.DataGrid.DataGridColumn1[[EventWithNavigationPropertiesDto, Application.Contracts, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].FormatDisplayValue(EventWithNavigationPropertiesDto item)
at Blazorise.DataGrid._DataGridRow`1.<>c__DisplayClass0_0[[EventWithNavigationPropertiesDto, .Application.Contracts, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].b__2(RenderTreeBuilder __builder3)
at Microsoft.AspNetCore.Components.Rendering.RenderTreeBuilder.AddContent(Int32 sequence, RenderFragment fragment)
at Blazorise.TableRowCell.BuildRenderTree(RenderTreeBuilder __builder)
at Microsoft.AspNetCore.Components.ComponentBase.<.ctor>b__6_0(RenderTreeBuilder builder)
at Microsoft.AspNetCore.Components.Rendering.ComponentState.RenderIntoBatch(RenderBatchBuilder batchBuilder, RenderFragment renderFragment)
at Microsoft.AspNetCore.Components.RenderTree.Renderer.RenderInExistingBatch(RenderQueueEntry renderQueueEntry)
at Microsoft.AspNetCore.Components.RenderTree.Renderer.ProcessRenderQueue()

[stsrki]

Is this a typo? The field name is LiveStreamPrice, but you defined it as LivePrice(EventPriceInfo.LivePrice).

[sturlath]

No, sorry that was just a typo. I was just simplifying the code (there is lots of other columns in there).
If I remove this column code there is no error. And if its not null and there is value in LivePrice it just works fine.

So still an issue :-)

[stsrki]

@David-Moreira Can you look into this, please?

[David-Moreira]

There were some iterations but since the first commit it's like this:

So basically if the property we are accessing is Nullable value type, it handles it appropriately.

Here, the use case @sturlath exposed, might seem easy at first glance, but it's a bit more complex.

The null check isn't at the end of the traversal, as it is for a Nullable<T> where T : Struct, but it is as we are navigating the property/field "tree" constantly checking for a null reference type. And actually having to actually return a valid value for the property we are accessing at the end of the traversal, which will most likelly be a ValueType and need to be set to it's default.

Basically having to build the expression correspondent to this type of null coalescing:
Parent1?.Parent2?.Parent3?.PropertyIWantToAccess

Since that wasn't initialy supported I would attempt this for 0.9.5 so we don't mess with the "expression compiler" in 0.9.4.

[stsrki]

I agree. We need to do this for 0.9.5.

[sturlath]

@stsrki just to follow up on this. Will this be fixed for 0.9.5?

[stsrki]

Yes, I believe @David-Moreira already fixed it.

[sturlath]

Found it #2855